1. Field of the Invention
The present invention relates to a process for preparing a 1-bromoallkylbenzene derivative. The invention also relates to a process for preparing an allyl Grignard reagent which can be an intermediate of the 1-bromoallkylbenzene derivative.
2. Description of the Related Art
1-Bromoalkylbenzene derivatives are useful substances as intermediates for medicines, agrochemicals, etc. For example, they can be important intermediates of the compound of the formula: ##STR1## which is useful as a medicine.
A 1-bromoalkylbenzene derivative of the general formula: ##STR2## wherein R represents a hydrogen atom, a lower alkyl group or a lower alkoxy group, and n is an integer of 1 to 8, may be prepared by reacting a phenylalkene derivative of the general formula: ##STR3## wherein R and n are the same as defined above, with hydrogen bromide. However, when the reaction of the phenylalkene derivatives of the general formula (X) with hydrogen bromide is carried out by conventional methods, for examples, using (1) an aqueous hydrobromic acid solution, or (2) a hydrobromic acid solution in acetic acid or propionic acid, there are problems that the reaction does not proceeds, or the selectivity of the 1-bromoalkylbenzene of the general formula (IX) is low and the isomer the general formula: ##STR4## wherein R and n are the same as defined above, is by-produced.
On the other hand, it is known to prepare the phenylalkene of the general formula (X) in which R is H and n is 2 in the following two ways: One process comprise the step of reacting phenetyl magnesium bromide with vinyl chloride in the presence of nickel acetylacetonate to obtain 4-phenyl-1-butene. The other process comprises the steps of reacting toluene with 1,3-butadiene in the presence of sodium to form 5-phenyl-2-pentene and then reacting it with ethylene in the presence of tetrabutyl tin and rhenium oxide to obtain 4-phenyl-1-butene.
However, both of the above processes are not satisfactory since they use sodium which is difficult to handle industrially, or use expensive catalysts.
It is known to prepare an allyl Grignard reagent in the following two ways: One process comprises the step of adding one mole of allyl chloride to 2.4 moles of magnesium in tetrahydrofuran which is cooled to -15.degree. C. over a period of 12 hours to obtain allyl magnesium chloride. The other process comprises the step of adding dropwise one mole of allyl bromide to 2.4 mole of magnesium in tetrahydrofuran which is cooled to 0.degree. C. over a period of 17 hours to obtain allyl magnesium bromide.
However, the processes use a large amount of the solvent, require the long periods of reaction time at the low temperatures and, in addition, are difficult to obtain the products in high yields since Wurtz-type reactions proceed rapidly (see Org. Syn., Coll. Vol. IV, p 749).